Cardiology In Critical Care
The SA pacemaker is suppressed or its impulses are blocked and the heart is controlled by impulses originating at the AV junction. Such impulses spread to the ventricles and also to the atria (in retrograde fashion). P waves are negative L2 and positive AVR and occur regularly at a rate 40-60. Depending upon whether retrograde conduction to the atria is faster, slower or similar to antegrade conduction to the ventricles, P waves either precede QRS complexes, the PR interval is less than 0.12 sec or follow QRS complexes by no more than 0.20 sec or are buried in the QRS complexes. Occasionally there is a block above the junctional focus so that the atria are under the control of sinus or atrial impulses (AV dissociation).
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